Recently, from the reasons for the strength, the ability to protect products, the working aptitude, the advertising effects by printing and others of wrapping materials, composite flexible films comprising a combination of different types of polymer materials have become the mainstream thereof. Such a composite film generally comprises a thermoplastic plastic film layer or the like to be the outer layer having the role of product protection and another thermoplastic plastic film or the like to be a sealant layer; and for laminating these layers, employed is a dry lamination method comprising applying an adhesive to a laminate film layer followed by adhering a sealant layer thereto, or an extrusion lamination method comprising adhering under pressure a plastic film to be a sealant layer, which has been optionally coated with an anchor coat layer and fused, to a laminate film layer. As the adhesive to be used in these methods, the mainstream is a two-component polyurethane-based adhesive that comprises a main agent having an active hydrogen group, such as a hydroxyl group or the like and a curing agent having an isocyanate group, from the viewpoint of high adhesiveness thereof (for example, see Patent Reference 1, Patent Reference 2).
However, in general, the curing reaction with such a two-component polyurethane-based adhesive of the type is not so high, and therefore, curing acceleration through long-term aging for from 1 to 5 days is needed after lamination, for securing sufficient adhesiveness. In addition, in this, a curing agent having an isocyanate group is used, and consequently, in case where an unreacted isocyanate group has remained after curing, the remaining isocyanate group would react with moisture in air to generate carbon dioxide, therefore providing a problem in that bubbles would be formed in the laminate film.
On the other hand, as a method for solving the problems, Patent Reference 3 proposes a specific polyurethane-based adhesive for dry lamination, and Patent Reference 4 proposes an epoxy-based adhesive for lamination.
However, the gas barrier properties of the polyurethane-based adhesives in Patent References 1 to 3 and the epoxy-based adhesive proposed by Patent Reference 4 are not high, and therefore, in case where a gas barrier properties is required for wrapping materials, it is necessary to additionally laminate various gas barrier layers, such as a polyvinylidene chloride (PVDC) coat layer, a polyvinyl alcohol (PVA) coat layer, an ethylene-vinyl alcohol copolymer (EVOH) film layer, a metaxylyleneadipamide film layer, an inorganic substance-deposited film layer with an alumina (Al2O3), silica (Si) or the like deposited thereon, etc. For these reasons, the adhesives have some disadvantages in point of the production cost for laminate films and the working steps in lamination therewith.
On the other hand, epoxy resin has many excellent characteristics, such as adhesiveness to various substrates, heat resistance, chemical resistance, electric properties, mechanical properties and others, as compared with other resins, and is therefore widely utilized in various industrial fields of civil engineering and building adhesives, etc. In general, the gas barrier property of the epoxy resin composition for use in an adhesive field is good as compared with that of urethane resin, acrylic resin, polyolefin resin, etc., but could not come up to that of polyvinylidene chloride, polyvinyl alcohol and the like falling within a group of gas barrier materials. Accordingly, in case where an epoxy resin is used, various attempts of increasing the thickness of the coating film, overcoating with any other material, using a filler in combination or the like are made for the purpose of enhancing the gas barrier capability thereof.
As an epoxy resin composition having a gas barrier property, Patent Reference 5 proposes an epoxy resin composition comprising an epoxy resin and amine-based curing agent. The epoxy resin composition could reveal a good performance in point of gas barrier capability, but further improvement thereof is desired these days, and in addition, the epoxy resin composition is insufficient in point of adhesiveness to polyester and aluminium that is desired to be improved.